Surgical cables are used in many surgical procedures. They are generally used to encircle the bone alone, or the bone and a bone plate, to facilitate fixation of one or more bone fragments. Some bone fixation systems that use surgical cable also use a bone plate having a length sufficient to span the bone fragments, fixation screws to couple the bone plate to the bone, adapters to couple the cable to the bone plate, and crimp devices for securing ends of the cable. In these systems, the surgical cable is generally coupled to the bone or the bone plate at 90° from the longitudinal axis of the bone.
Because the surgical cable is wrapped around the bone and bone plate, as forces act on the cable, the cable may tend to move from its coupled position with respect to the bone plate. As such forces act on the cable, a longitudinal axis of the cable will generally tend to be angled at less than 90° from the longitudinal axis of the bone. This may result in shear stresses and strains in the surgical cable that cause the bone plate to shift relative to the bone.
Some fixation screws function to both couple the bone plate to bone and serve as a means for coupling the cable at a certain position along a length of the bone plate. If the fixation screws are used to couple the cable to the bone plate, then the cable is generally received in a slot or bore in a head portion of the fixation screws. Such fixation screws also act as an adapter. The head portion of the fixation screws are generally integrally coupled to a shaft of the fixation screws but may be a separate component that is coupled to the shaft of the fixation screws.
The adapters and fixation screws explained above generally function to prevent migration of surgical cable along a longitudinal axis of a bone plate. These systems do not, however, provide a means of orienting the surgical cable at an angle less than 90° from the longitudinal axis of the bone. Therefore, they cannot sufficiently eliminate the stresses and strains in the surgical cable which may cause shifting of the bone plate.